Fluid cooled electrical apparatus combined with response-compensated temperature measuring device



MEASURING DEVICE Filed June 23, 1950 June 29, 1954 Irwventor:

we n O w mm QoH uy Patented June 29, 1954 UNITED STATES PATENT OFFICE FLUID CO OLED ELECTRICAL APPARATUS COMBINED WITH RE SPONSE- COMPEN- SATED TEMPERATURE MEASURING DE- VICE Guglielmo Camilli, Pittsfield,

General Electric Company,

New York Application June 23,

4 Claims.

former. The degree of heat in the heating coil surrounding the thermal-responsive element is proportioned to the amount of current flowing Mass., assignor to a corporation of 1950, Serial No. 169,984 (Cl. 73-350) is much greater for a static liquid condition than for a flowing liquid condition, since the heat transfer from the electrical winding at any given It is an object of my invention, therefore, to provide an automatic calibrating means for use with a liquid-immersed thermal-responsive element which Will automatically compensate the indications of the thermal-responsive element for failure in the circulatory system of a liquidcooled electrical apparatus, such as 'a transformer.

circulatory system fails.

The features of this invention which I believe set forth with particularity in to be novel are the appended claims. My invention itself, howsure-responsive the circuit of element.

Referring now to the drawing, there is shown a transformer casing l in which is contained a transformer winding 2 positioned on a magnetic core 3. Insulating bushings 4 and 5 pass through the top surface of tank l and serve to insulate the conductors which lead from the winding .2 to the external circuits to which winding 2 is connected. The interior of transformer tank i is filled with a suitable cooling and insulating liquid 6, such as oil, for example, to a level above the top of the transformer core. A pump 1 is provided, preferably on the exterior of the transformer tank, to provide forced circulation of the oil through the transformer tank and also through any cooling devices which may be provided. These cooling devices are not illustrated in the drawing but may take any suitable form, such as, for example, radiator tubes mounted on the outside surface of the tank. The pump 1 communicates with the upper and lower surfaces of the interior of the tank 1 by means of conduits 8 and 9 respectively.

In order to provide a suitable indication of the temperature of winding 2, a thermal-responsive element Iii, which, in this case, is a bulb contain ing a. volatizable fluid, is contained in a well member ii positioned interiorly of tank l. The thermal-responsive element It is connected to any suitable indicating or relay device H which is located at some point exterior of the transformer tank. Since the particular thermal-responsive element shown is a bulb containing volatilizable fluid, a capillary tube i3 is used to connect the thermal-responsive element if) to the indicating or relay device l2. The well i l in which thermalresponsive element ill is enclosed is surrounded on at least part of its exterior surface by a heating coil M which is energized by a current transformer ill in series with one of the conductors leading to winding 2.

The heating coil l4 may be adjusted in such manner that the temperature indicated by indicating device l2 corresponds to the calculated temperature of the copper conductors on winding 2 at any given load on the transformer. Thus, the thermal-responsive element ill will simulate the thermal conditions present in the transformer winding 2. However, for a forced flow cooling system, this initial adjustment or calibration is made on the basis of a continuously circulating liquid flow, and failure of such liquid flow will produce erroneous readings at the indicating de vice I2.

In order to compensate for any error which would be introduced into the readings of indicating device 62 by failure of the liquid circulatory system, I have provided a compensating means in accordance with my invention which will now be described.

In accordance with my invention, a pressuresensitive element, such as a bellows I6, is hydraulically connected to the liquid flow system, preferably near the outlet of pump 1. The pressure-sensitive device it is provided with a contact arm ll which moves with the bellows. Contact arm H is adapted to bridge contacts 18 and [9 when the hydraulic pressure of the liquid circulatory system causes bellows Hi to move to its fully expanded position. When contact arm i1 bridges contacts l8 and IS, a resistance element 20 is inserted in parallel with heating coil M, and diverts part of the current output of current transformer I5 away from heating coil l4. When this situation prevails, the current through heating coil 14 for a given current through the transformer I5 is less than when the circuit of resistance element 20 is open, and, consequently, the heat given off by heating coil i4 is less. However, if the liquid pressure of the circulatory system decreases for some reason, such as a pump failure, bellows 16 will move to a contracted position and contact arm l1 will no longer bridge contacts 18 and I9. When this happens, the circuit of the resistance element 20 is opened, and all of the current through the secondary of current transformer l5 passes through heating coil 14. For a given load current passing through the primary of the current transformer, the heating coil it then gives off more heat. Opening the circuit of shunting resistance 20 when the circulatory system fails will result in a changed reading of indicating device l2. For a given transformer or other apparatus, the increase in winding temperature when the pump is not operating can be calculated, and the value of resistance element 2% can be made of such value as to cause indicating device if to give a proper reading of the increased temperature when the pump is not operating. The necessary value of the resistance to be added will also depend on the effect, if significant, of circulation failure on the heattransfer relation between heating coil l4 and element iii.

In Fig. 2 l have illustrated a modified form of my invention for use with a resistance-type thermal-responsive element. There is shown in Fig. 2 a, thermal-respcnsive resistance element 21 contained in a well member 22 positioned interiorly of the tank for an electrical apparatus. The

thermal-responsive resistance element is connected to an suitable indicating or relay device it by means of leads 24 and 25 which are respectively connected at opposite ends of thermalresponsive resistance element 21. The well 22 in which thermal-responsive element 2| is enclosed is surrounded on at least part of its exterior surface by a heating coil 26 which is energized by a current transformer 21 in series with one of the conductors leading to the electrical apparatus.

In accordance with my invention, the pressuresensitive element, such as a bellows (not shown in this figure), operates a contact arm 28. Contact arm 23 is adapted to bridge contacts 29 and 30 when the hydraulic pressure of the liquid circulatory system causes the pressure-sensitive element to move to its fully expanded position. When contact arm 28 bridges contacts 29 and 30, a resistance element 3| in series with thermalresponsive resistance element 2| is shorted out and has no effect on the action of control or indicating device 23. However, if the liquid pressure of the circulatory system decreases for some reason, such as a pump failure, the pressure-responsive device will move to a contracted position and contact arm 28 will no longer bridge contacts 29 and 30. As a result, resistance element 31 is no longer shorted and is inserted in the circuit with thermahresp 'onsive resistance element 2|. Introduction of resistance element 31 into the circuit of indicating device 23 will result in a changed reading of indicating device 23. For a given transformer or other apparatus, the increase in winding temperature when the pump is not operating can be calculated, and the value of resistance element 3| can be made of such value as to cause indicating device 23 to give a proper reading of the increased temperature when the pump is not operating. The necessary value of the resistance to be added will also depend on the effect, if significant, of circulation failure on the heat-transfer relation 2. The cooling arrangement of claim 1 wherein between heating coil 26 and element 2|. the electric heating element is in the form of a From the foregoing, it can be seen that I have coil immersed in the cooling fluid and surroundprovided a new and improved device for coming a portion of the temperature measuring pensating for false temperature indications when 5 device.

the liquid circulation system of an electrical 3. The cooling arrangement of claim 1 wherein apparatus such as a transformer is not in operathe auxiliary circuit is connected by a switch tion, due to some reason such as a pump failure. operated from a fluid-pressure-sensitive device While there have been shown and described connected to the circulating means. particular embodiments of my invention, it will 4. In combination, an electrical apparatus all such changes and modifications as fall within cator means actuated by said thermal-responsive the true spirit and scope of the invention element a heating 0011 in heat exchange relation What I claim as new and desire to secure by to said liquid and to said thermal-responsive ele- Letters Patent of the United States is: ment, said heating coil being energized by heating 1. In a cooling arrangement for electric appa- I current in accordance with the electrical current ratus immersed m a flllld, circulating means 0 flowing in said electrical apparatus so as to reflect Whleh said electric apparatus is immersed Where accordance with the changed thermal condition by the mdleetlen of said temperature measurof said electrical apparatus induced by said cirmg devlce 1s mdlcatlve of the temperature of the culation failure, said pressure-sensitive means eleetne apparatus when said fl d elreulatmg normally maintaining said shunting resistance in cuit including a resistance adapted to reduce the circulating means causing said pressure-sensitive energization of said electric heating element m w to m u a Qlrectlon as to Open the when the said circuit is connected with said elecclrcult of sald shuntmg reslsta'ncecompleted to reduce the energization of said References cued m the file of thls patent heating element when said fluid circulating 40 UNITED STATES PATENTS means is in operation, and means adapted to open Number Name D t said auxiliary circuit in response to the non- 1,477,456 Simmon Dec. 11, 1923 operation or said fluid circulating means whereby 1,835,470 Clarke Dec. 8, 1931 the energization of said heating element is in- 1,379,276 Isaac Sept. 27, 1932 creased consonant with the increased tempera- 415 2,026,375 Camilli Dec. 31, 1935 ture of the fluid in which said electric apparatus 2,349,673 Pearson et al May 23, 1944 is immersed to enable said temperature measuring device to continue to reflect the temperature FOREIGN PATENTS of said electric apparatus when said fluid circu- Number n y Date lating means non-operative. 025 Great Britain Apr. 30, 1941 

